Long before DNA, enzymes, or cell membranes evolved, RNA may have played a dual role as both genetic material and catalyst. This possibility forms the basis of the RNA World hypothesis, one of the leading explanations for how life began. In short, that is the essence of the theory called RNA World hypothesis, the single most respected framework within origins-of-life science. The concept is predicated upon a remarkable observation that RNA, unlike any molecule used in biochemistry today, is capable of performing two functions. RNA has the ability to store genetic information in the same manner as DNA, as well as the ability to catalyze reactions in the same way as enzymes.
The trouble with demonstrating that RNA could reproduce itself in the lab under prebiotic conditions has always been the biggest issue facing researchers into the origins of life. A paper published in Nature Chemistry in May 2025 by Dr James Attwater and Dr Philipp Holliger at the MRC Laboratory of Molecular Biology in Cambridge describes what they call the first successful demonstration of exponential, open-ended RNA replication under conditions that could plausibly have existed before biology existed to help.
What they solved is called the strand separation problem. And understanding why that problem is so hard is the key to understanding why this result matters.
The RNA world hypothesis states that the earliest self-replicating entities consisted of RNA molecules, rather than DNA. DNA stores genetic information, but its replication depends on complex protein machinery. Proteins, in turn, require genetic instructions encoded in nucleic acids. In turn, proteins cannot make themselves; genetic information is needed, supplied by nucleic acids, to build them. This is the chicken-and-egg problem at the heart of life's origin. Which came first?
In contrast to the DNA situation, some RNA molecules known as ribozymes have the capability of folding into three-dimensional structures capable of catalyzing a reaction, including RNA copying. The ability of RNA to replicate itself would make it capable of transferring genetic information through subsequent generations while remaining independent of non-existent proteins that perform this function in living things today. Life could, in theory, start with RNA alone.
For such a cycle to take place, RNA replication needs to occur exponentially, meaning that replicated molecules will replicate again and again, forming an unlimited chain. This was exactly where scientists found themselves unable to proceed with their research before.
When an RNA molecule is copied, the resulting double-stranded RNA consists of the original template strand and its newly synthesised complement. In today’s cells, protein enzymes called helicases use energy from ATP hydrolysis to pull these two strands apart, freeing them to serve as templates for the next round of replication.
On the early Earth, before proteins existed, there were no helicases. The RNA duplex, once formed, simply stayed zipped together. And RNA duplexes are extraordinarily stable and fast-forming, described aptly in the paper's abstract as exhibiting the behaviour of velcro: they zip shut quickly and are difficult to pull apart. Any RNA copies produced were effectively trapped in double-stranded form before they could be used as templates for the next generation.
This is product inhibition in the most straightforward sense. The product of replication, the double-stranded duplex, blocks the process from continuing. Previous laboratory work had demonstrated that RNA polymerase ribozymes could copy RNA strands, and had made steady progress on fidelity and strand length. What no one had achieved was a full replication cycle that could turn over: copy a strand, separate the copies, and copy them again, repeatedly, without any protein assistance.
The solution came from two innovations working together: a different kind of building block, and a different kind of environment.
Instead of using single nucleotides, the standard building blocks of RNA synthesis, the team used trinucleotide triphosphates: building blocks made of three RNA letters joined together. These do not occur in biology today. The team's reasoning was that trinucleotides would coat newly separated RNA strands and hold them in a single-stranded state, physically preventing them from zipping back together before replication could occur.
For the environment, the team used a freeze-thaw cycle driven by alternating pH and temperature. RNA strands in solution were first exposed to acidic conditions and heat, which separated the double helix. The solution was then neutralised and frozen. In the thin liquid channels that form between ice crystals during freezing, trinucleotides concentrated around the separated strands, holding them open. Replication by the RNA polymerase ribozyme then proceeded in those liquid veins. Thawing, repeating, thawing again: the cycle drove exponential replication over multiple rounds.
The proposed real-world setting for this chemistry is a geothermal freshwater pool, where heat from underground rock meets a cold surface atmosphere, producing natural freeze-thaw cycles across daily temperature fluctuations. Saltwater does not work: salt disrupts the freezing geometry and prevents the concentration effect from building up. The geography implied is a cold-climate volcanic freshwater environment, not an ocean.
It is worth being precise here because the RNA world literature is active and results are easy to conflate. A 2024 paper from Gerald Joyce's group at the Salk Institute demonstrated a ribozyme capable of copying RNA with significantly improved accuracy. That work addressed fidelity: how accurately RNA can be copied. A separate line of work from Holliger's own group, published in early 2026, described a ribozyme called QT45 capable of synthesising both itself and its complementary strand, though not yet simultaneously in one pot.
The May 2025 paper addresses a different problem: not fidelity, and not the capacity to copy RNA at all, but the turnover problem. Without strand separation, replication has no second generation. The trinucleotide-freeze-thaw approach provides a physical, protein-free solution to exactly that bottleneck. Both the positive and negative strands of the duplex were replicated. The system was applied to random RNA sequence pools. Sequence composition gradually drifted toward what the authors describe as hypothesised primordial codons, early precursors to the genetic code.
The paper does not explain how life began. The authors do not claim otherwise. Dr Attwater is quoted in the UCL press release noting that even the Last Universal Common Ancestor of all known life, called LUCA, is a complex entity with extensive evolutionary history hidden behind it. The experiment provides a plausible mechanism for one specific step, strand separation during RNA replication, in one plausible environment. It does not reconstruct the full chain of events from chemistry to biology.
The trinucleotide building blocks used in the experiment are not found in biology today. The researchers argue they could have been present in prebiotic chemistry and later replaced by single nucleotides as biology became more sophisticated, but this remains a hypothesis. The geothermal freshwater setting is plausible but not confirmed as the actual site of life's origin. Competing hypotheses, including deep-sea hydrothermal vents and warm little ponds of the kind Darwin speculated about, remain viable.
The RNA world hypothesis itself is not proven by this paper. It is strengthened, specifically at one previously problematic step. The debate about how life began will continue, as it should.
Why This Finding Matters for Science:
First demonstration of open-ended exponential RNA replication without protein machinery
Solves the strand separation problem, a bottleneck that had blocked origins-of-life research for decades
Trinucleotide building blocks physically prevent double-stranded re-zipping, enabling multiple replication rounds
Freeze-thaw cycles in geothermal freshwater pools provide a plausible early Earth environment for this chemistry
Sequence drift toward primordial codons suggests a possible link between RNA replication and the origin of the genetic code
Does not prove the RNA world hypothesis or explain how life began: it resolves one specific mechanistic obstacle
Does this mean scientists have created life in a laboratory?
No. The experiment demonstrates a mechanism for RNA self-replication under prebiotic conditions. Creating life requires far more than replication: it requires a membrane, a metabolism, and a functional genetic code, none of which were part of this study.
What is a ribozyme and why does it matter here?
A ribozyme is an RNA molecule that can catalyse chemical reactions, functioning like a protein enzyme. The existence of ribozymes is central to the RNA world hypothesis because it means RNA can potentially perform both the informational and catalytic roles required for self-replication, without proteins.
Why does the experiment use freezing? What does ice have to do with the origin of life?
Ice is not incidental to the experiment. The thin liquid channels between ice crystals act as a natural concentrating environment, bringing RNA molecules and trinucleotide building blocks close together. The Attwater-Holliger group has been exploring ice as a prebiotic medium since at least 2010. The proposed setting is a cold volcanic freshwater pool, not a frozen ocean.
Is the RNA world hypothesis now proven?
No. This paper strengthens the hypothesis by solving one previously unresolved mechanistic step. The RNA world hypothesis remains the most widely supported framework for the origin of life, but it is not experimentally confirmed as the historical pathway life actually took.
Attwater, J., Augustin, T. L., Curran, J. F., Kwok, S. L. Y., Ohlendorf, L., Gianni, E., & Holliger, P. (2025). Trinucleotide substrates under pH-freeze-thaw cycles enable open-ended exponential RNA replication by a polymerase ribozyme. Nature Chemistry, 17(7), 1129-1137. https://doi.org/10.1038/s41557-025-01830-y
Horning, D. P., & Joyce, G. F. (2016). Amplification of RNA by an RNA polymerase ribozyme. Proceedings of the National Academy of Sciences, 113(35), 9786-9791. https://doi.org/10.1073/pnas.1610103113
Attwater, J., Wochner, A., & Holliger, P. (2013). In-ice evolution of RNA polymerase ribozyme activity. Nature Chemistry, 5(12), 1011-1018. https://doi.org/10.1038/nchem.1781
Gilbert, W. (1986). Origin of life: The RNA world. Nature, 319(6055), 618. https://doi.org/10.1038/319618a0
University College London. (2025, May 29). Chemists recreate how RNA might have reproduced for first time. ScienceDaily. https://www.sciencedaily.com/releases/2025/05/250528132057.htm
